The present invention relates to a solid electrolyte fuel cell and more particularly to a solid electrolyte fuel cell including a cathode layer formed on one surface of a solid electrolyte layer and an anode layer formed on the other surface of the solid electrolyte layer.
Patent Reference 1 proposes a simple fuel cell which can be disposed in or in the vicinity of burning flame to generate electricity. This fuel cell is shown in FIG. 8. A fuel cell 100 shown in FIG. 8 is a solid electrolyte fuel cell (hereinafter referred to as “solid electrolyte fuel cell 100”) including a cathode layer 104 formed on one surface of a solid electrolyte layer 102 having a dense structure and an anode layer 110 formed on the other surface of-the solid electrolyte layer 102. The cathode layer 104 and the anode layer 110 each are in the form of a porous layer having mesh metals 106 and 112 embedded therein or fixed thereto, respectively. Extending from the mesh metals 106 and 112 are lead wires 108 and 114, respectively.
[Patent Reference 1] JP-A-2005-63686
The solid electrolyte fuel cell 100 shown in FIG. 8 can be disposed in such an arrangement that the anode layer 110 side surface thereof is in or in the vicinity of burning flame to generate electric power that can be drawn out through the lead wires 108 and 114.
However, when the solid electrolyte fuel cell 100 shown in FIG. 8 is repeatedly exposed to flame on the anode layer 110 side surface thereof, a phenomenon occurs that the electric power taken out through the lead wires 108, 114 gradually decreases, demonstrating that it lacks durability. Further, the electric power taken out through the lead wires 108, 114 is insufficient. It has thus been desired to enhance the durability and electric power of the solid electrolyte fuel cell 100 shown in FIG. 8.
The inventors thought that the reason for the insufficient durability of the solid electrolyte fuel cell 100 shown in FIG. 8 is the exfoliation of the cathode layer 104 of the porous layer and the dense solid electrolyte layer 102 from each other on their interface due to the difference in thermal expansion coefficient between them. The inventors then attempted to form the cathode layer by an electrode material and an electrolyte material in admixture in order to minimize the difference in thermal expansion coefficient between the cathode layer and the solid electrolyte layer.
In order to form a cathode layer by an electrode material and an electrolyte material in admixture, the mixing ratio of the electrode material and the electrolyte material is normally predetermined to be from 70:30 to 80:20. Then, the inventors prepared a solid electrolyte fuel cell including a cathode layer made of an electrode material and an electrolyte material at amixing ratio of 50:50 having a mesh metal embedded therein provided on one surface of a dense solid electrolyte layer.
The solid electrolyte fuel cell thus prepared exhibits an enhanced durability but shows little or no enhancement of electric power output as compared with the solid electrolyte fuel cell 100 shown in FIG. 8. The reason for this phenomenon is presumably because the cathode layer formed by an electrode material and an electrolyte material at a mixing ratio of 50:50 has a dense structure that decreases the transfer resistance of oxygen ions to the dense solid electrolyte layer but decreases the area of the three-phase interface on which the gas such as oxygen, the electrode material and the electrolyte material come in contact with each other.
It is also made obvious that the solid electrolyte fuel cell thus prepared shows a deteriorated adhesion of the mesh metal due to the difference in thermal properties between the mesh metal embedded in the cathode layer and the electrode material.